How often does someone emit gas per day (fart) or how much should they?

Farty times a day. As often as necessary. Most flatulence is a result of diet and of the natural flora or friendly bacteria that live in your colon. Flatulence is a natural bodily function, so don't fret it.
Average 14... Yes there is a gastroenterologist - clearly one with a sense of humor - who has studied this in the usa. The average is 14 which means less for some people and more for others. Enjoy!